1. Field of the Invention
The present invention relates to a surface treatment process for the corrosion protection of neodymium-iron-boron group sintered magnets.
2. Prior Art
Neodymium-iron-boron group magnets are rare-earth magnets having high magnetic flux density and high coercive force and are in great demand. However, this type magnets corrode easily. Furthermore, this type magnets have a tendency to be embrittled with absorption of hydrogen produced in corrosion reaction caused by the fact that neodymium is a strongly hydrogen absorbing metal. Therefore, the establishment of a perfect corrosion protection process has been required because the conventionally known process has the following disadvantages.
If corrosion protection plating such as zinc plating or cadmium plating is applied to the neodymium-iron-boron group sintered magnets, embrittlement occurs with absorption of hydrogen produced during electrolysis. If electrostatic painting or powder coating is applied to this type magnets, water penetrates paint film to react on the base metal thereof. If cationic electrodeposition coating which is, in general, a coating process most excellent in corrosion resistance is applied, sufficient corrosion protection effect cannot be obtained.